It is proposed to study the ontogeny of the immune response with regard to the ability of B lymphocytes to produce a heterogeneous antibody response. Heterogeneity will be assayed by evaluation of heterogeneity of affinity of plaque forming cells by hapten inhibition. Studies will be carried out in cell transfer systems. The kinetics of maturation of the ability to give a heterogeneous response will be followed. Genetic control and other factors influencing the maturation process will be explored. BIBLIOGRAPHIC REFERENCES: Goidl, E.A., Birnbaum, G. and Siskind, G.W. Determination of antibody avidity at the cellular level by the plaque inhibition technique: Effect of valence of inhibitor. J. Immunol. Methods 8, 47-51, 1975. Goidl, E.A., Barondess, J.J. and Siskind, G.W. Studies on the control of antibody synthesis. VIII. Changes in affinity of direct and indirect plaque forming cells with time after immunization in the mouse: loss of high affinity plaques late after immunization. Immunology 29, 629-641, 1975.